1. Field of the Invention
The present invention relates to a power quality monitoring apparatus and a method thereof; and, more particularly to a power quality monitoring apparatus and a method thereof capable of detecting the quality of power such as a sudden voltage swell and sag.
2. Description of the Related Art
In conventional, electronic products such as a computer, a communication device, a medical device and a military device are load very sensitive to a power quality. Since such industrial, commercial and military loads are operated by being connected on an automatic process mutually, a power system connected thereto such loads has affected to the power quality very sensitively.
The power quality is classified into a voltage quality and a current quality; the voltage quality deals with states such as a voltage swell, a voltage sag, an under voltage, an over voltage, an interruption, a noise and other factor such as a DC offset, harmonics, inter-harmonics, notching, a voltage imbalance, a voltage fluctuation and a flicker and the like; and the current quality deals with a power interruption problem such as the distortion of the voltage according to the current distortion is generated as the nonlinear load is increased.
On the other hands, as the power quality monitoring apparatus is a means to monitor whether an erroneous operation is generated in a power system and load devices by being installed between power systems (power systems in the generation and transmission/distribution steps), that is, a power side and the load device, if the erroneous operation is generated in the power system and the load devices, it can prevent an accident in advance by protecting the power system and the load devices by blocking the circuits between the power system and the load devices or analyzing the power quality.
In order to this, the power quality monitoring apparatus according to the prior art converts the voltage and current signals of analog shapes into the digital data by sampling the analog signals, calculates an RMS (Root Mean Square) by using the converted digital data and employs a method to sense the generation of accidents through comparing the calculated RMS with the reference value.
However, although data above a minimum number of periods are required to detect the RMS in the power quality monitoring apparatus according to the prior art, but there is a problem difficult to detect since the change is nearly not in the RMS in case when the numerical value is changed during a short continuing time such as voltage swell and sag. That is, since the power quality monitoring apparatus according to the prior art takes a long time for calculating the RMS, it has a problem not to monitor the voltage swell and sag generated during a short continuing time such as a half period.